1. Field of the Invention
This invention relates to scanning continuously moving information bearing media to produce an image signal and, more particularly, to scanning continuously moving or stationary motion picture film frames to produce television signals therefrom, the scanning rate being responsive to the rate of movement of a motion picture film.
2. Description of the Prior Art
In telecine transmission systems, flying spot scanning devices have often been used to scan the frames of motion picture film in a scanning raster pattern to produce interlaced television fields representative of the scanned image frames. The scanning raster pattern light beam is modulated by the image pattern of the film frame, and the modulated light is detected and transformed into a video signal by photoresponsive devices. The transmitted video signal controls the electron beam of the television receiver tuned to the transmitting station to reproduce the motion picture film frame on the television screen. Since it is desirable that the motion picture film be moved continuously and transversely to the beam of light produced by the flying spot scanning device at its normally projected frame rate, it is necessary to deflect the scanning light beam in the direction of movement of the film at the field rate frequency. Therefore the frame area of the film scanned remains constant for each scaning field, and each frame is scanned by an integral number of scanning fields.
Prior art systems have used optical image splitting apparatus or mechanical light directing apparatus to deflect the scanning beams at the same point on the film frame during each scanning field. These systems are relatively cumbersome and subject to mechanical failure.
Further prior art systems contemplate the use of apparatus for applying a signal having an irregular amplitude, sawtooth wave form to the vertical deflecting coils of the flying spot scanning device to deflect the scanning light beam in the direction of film movement. Such systems may be, relatively expensive, and in many instances, are not directly synchronized to the actual rate of movement of the film frames.